The present invention relates to ultra-clean fluoropolymers, especially thermoplastic and elastomeric fluoropolymers, compositions incorporating such fluoropolymers, articles employing such fluoropolymers and methods of making and using such fluoropolymers.
High purity fluoropolymers are used in a number of industries. They are especially preferred for use in the electronic, semiconductor, optical, medical and pharmaceutical industries to name a few. These polymers have a relatively low level of extractable metals and metal compounds.
High purity fluoroelastomer compositions are known. See EP-B-0 708 797 which discloses an elastomer composition comprising
(A) a peroxide-curable elastomeric fluoropolymer,
(B) an organic acid acceptor,
(C) an organic peroxide,
(D) a coagent for the organic peroxide, and
(E) a fluoropolymer micropowder filler.
This composition is said to be free from carbon fillers and have less than 500 ppb of extractable metals and metal compounds. This low content of metals and metal compounds is achieved by selecting metal-free acid acceptors, coagents and fillers. The acid acceptors are generally strong organic bases.
It now has been found that high-purity fluoropolymers and corresponding fluoropolymer compositions are feasible even without the use of such organic acid acceptors. Thus the present invention comprises
a process for preparing salt-free fluoropolymers,
the so-obtained fluoropolymers,
compositions containing such fluoropolymers,
processes using such fluoropolymers or such compositions, and
articles of or coated with the said fluoropolymers or such compositions.
The said process for preparing salt-free fluoropolymers comprises
polymerizing one or more fluoromonomers by the aqueous emulsion polymerization process,
removing from the so-obtained latex essentially all ions different than NH4+, H+ and OHxe2x88x92, and
coagulating the fluoropolymer essentially without addition of ions.
The polymer of the invention comprises an emulsion polymerized fluoropolymer that is essentially free of all ions other than NH4+, H+ and OH31 .
The preferred fluoropolymer is either a thermoplastic or an elastomeric polymer. The preferred elastomeric fluoropolymer is a curable elastomer such as a peroxide-curable elastomer or an elastomer having pendent nitrile groups.
The curable fluoropolymer composition of the invention comprises the fluoroelastomer and an appropriate curing agent. When a peroxide-curable elastomer is used the curable elastomer composition comprises
a) a peroxide-curable fluoroelastomer that is essentially free of ions other than NH4+, H+ and OHxe2x88x92;
b) an effective amount of a peroxide curative for the fluoroelastomers;
c) optionally, and preferably, a coagent for the peroxide; and
d) optionally, a partially crystalline fluoropolymer that is preferably essentially free from ions other than NH4+, H+ and OHxe2x88x92.
When a nitrile group containing elastomer is used the curable elastomer composition comprises
a) a curable fluoroelastomer that has nitrile groups and that is essentially free of ions other than NH4+, H+ and OHxe2x88x92;
b) an effective amount of an ammonia generating cure system, and
c) optionally, a partially crystalline fluoropolymer that is essentially free of ions other than NH4+, H+ and OHxe2x88x92
The processes of using the polymers or polymer compositions of the invention include the steps of contacting a surface with the polymer or polymer composition and subsequently optionally causing the polymer or polymer composition to cure or otherwise become secure to the substrate.
The articles of the invention include
a) shaped articles comprising the cured elastomer composition of the invention, and
b) articles coated with the composition of the invention.